text:
Tips for the private pilot check ride
I am 17 and am going to be taking my check ride for my private pilot's license very soon. What tips do you have before I go up? (Oral exam and check ride).
I am more looking for personal experience and tips from people who have taken the check ride. I know what goes on during the check ride already, I'm looking for things people know would be useful from their own experience that they want to pass along.

Which country are you in?

I'm from the US

I'm not sure that What happens during a checkride for a private pilot license? really is a duplicate of this question. That question asks for the sequence of events, this is asking for tips on how to prepare. The two are definitely related, but I don't think it's the same question.

Yes, thank you. I am more looking for personal experience and tips from people who have taken the check ride. I know what goes on during the check ride already, I'm looking for things people know would be useful from their own experience.

Do NOT worry about getting an unsatisfactory result!!  It just does not matter.  There will be no record of it anywhere but in your memory.  It's not noted on your certificate and, really, nobody will care.  The PPL is a license to learn and that is what you'll be expected to do after you pass.  The checkride merely assesses basic requirements.  Now, if you want to be a professional pilot...it still doesn't matter.  Nobody will care if you made a dumb mistake on a PPL ride and had to go back and demonstrate a maneuver again.  Anyone who does is not worth working for anyway!
Think about it, worst case you have to go flying again (that's a pretty good "worst case").  The only downside I see is having to pay the examiner fee again.
Ok, but real advice...
1.) Get sleep the night before.  You'll be nervous, but sleep anyway.  You already know everything you need to know to pass, a few more hours of studying won't make or break the ride.
2.) It's ok to say "I don't know the answer, but I know where to find it," and then look it up.  You can't say it for every answer, but it's not a deal breaker to not know something.
3.) At least one experienced pilot (your CFI) thinks you're ready to be a PPL.  If you took a stage check with an evaluators at a flight school, two experienced pilots think you've got what it takes.  CFIs don't sign off on a checkride if they think the student will fail.
4.) Be able to explain why the plane is legal to fly.  One of the examiners I used loved to ask the students to prove that the plane was legal.
5.) Be able to explain why you're qualified to take the exam.  The same examiner would routinely ask students to prove that they were qualified to take the exam.
The only way this ends is with you earning a PPL.  If it takes two rides, so what?  You've already done the hard work.  Just go flying with the examiner and show him/her what you've been showing your instructor for the past few hours.
Good luck.  Don't sweat it.

Its a bit out of date but this video is a good resource.
All check rides are a bit different since the DPE has some room in what he can/does do. However the FAA does require particular things. Many people (myself included) got their tickets when the older PTS's were in place. You will be tested under the new ACS regulations but they are quite similar from what I understand.
As some general advice,
Whats most important is that you answer to the best of your ability and be sure to provide as many references as you can. Don't be afraid to say

"I don't know the answer but I know where to look to find it"

In many cases this is what the DPE is looking for. Don't be afraid to pull out the FAR and point to a specific regulation for particular wording or a particular number etc. Showing that you know how to use the FAR's as a tool and can quickly navigate them is key. You are not expected to know every single regulation in the book but you are expected to know that you can find them all in there.
Along with having positive control of the plane (don't let the aircraft get ahead of you) you should know your plane and its POH inside and out. Have the performance charts tabbed with a post-it or something so you can quickly turn to them as you are going to need them. You may want to notate other common numbers in the POH so you can get to them fast.
Have your emergency checklists at hand. Make sure to read them out and mime the maneuvers on your power off landing. The FAA is having examiners stress certain things and this is one of them.
Some healthy confidence will go a long way, if you are asked about what to do in a situation explain why you are taking said course of action and be ready to back it up.
Examiners love to trick you but they are also not out to get you. They have a few hours to make sure you are a good decision maker and a half decent pilot its stressful for them as well. They are putting plenty on the line when then sign you off as well. Show them you are a good decision maker above all.

I actually have that video open right now! Haha Thank you

As a generic answer, you will want to thoroughly read the Private Pilot - Airplane Airman Certification Standards.  This document is the benchmark for the skills which you will have to demonstrate to the examiner in order to pass.  Read through it and thoroughly review it.  If you are concerned that you cannot perform a skill to the standards listed here, talk with your CFI and go up for another practice flight to work on these areas prior to your practical.
Other tips:
First off, as discussed above, make sure that, not only can your perform the skills listed above, but that you can do them in an unconsciously competent manner.  They don't have to be perfect, but be able to demonstrate them to an examiner, to the standards listed above, all while being subject to other environmental stressors - radio chatter, examiner small talk/comments, changes in plans, etc. which are adding to your workload and you have to consciously think about.
Find out who the examiner will be and talk with other pilots to get a feel for this person.  Is this person fairly easy to work with?  Are they spiteful and just search for ways to trip up and fail a student?  The practical will be demanding enough without the DPE acting this way and adding to your stress level.
IMSAFE - Illness, Medication, Stress, Alcohol, Fatigue, Eating/Exercise.  Make sure that you can meet these guidelines to make you body as physically prepared for the checkride as possible.  Make sure you are not ill and take steps eg wash your hands regularly, stay away from sick people, etc for the preceding week or so before the checkride.  Make sure you are not on any medications which will interfere with your ability to operate a motor vehicle or serve as PIC.  Avoid stressful situations a few days before the checkride and terminate all studying for the practical at least 12 hours before it is scheduled to avoid burnout.  Don't drink or take drugs (duh!) before a check ride.  Make sure you get plenty of exercise on the week of the checkride.
And on sleep - GET AT LEAST 8 HOURS OF SLEEP THE NIGHT BEFORE THE CHECKRIDE.  Do so in a totally dark, silent and cool room.  Turn off and abstain from using computers and portable electronics, smartphones, and tablets at least one hour before bedtime; the blue light from the screens really screws up your circadian rhythm and almost guarantees you light and restless sleep - not good.  Eliminate any kind of distractions and do not drink caffeinated beverages at least 3-4 hours before bedtime.
Keep an eye on the weather forecast for the day of the flight.  Select days which there will be good visibility and light winds.  Even if the conditions are VFR, strong winds are likely to make the landings - especially crosswind landings - very treacherous.  You don't want to do an otherwise perfect checkride and then bust it when the plane slams down during landing.  If the weather just isn't cooperating with the planned day of the checkride, just re-schedule it.  This happens a lot in GA and also the DPEs like it as it demonstrates both a consciousness of weather conditions and a refusal to be rushed and carry out a flight in adverse conditions, something that a lot of pilots do which is just asking for trouble.
Get to the airport early and make sure everything is ready to go.  Verify the airplane is available and do a pre-flight check (your examiner will ask you to do a second one) to make sure nothing is wrong with the a/c and it is ready to fly.  Identify the room where you will be doing the oral exam and make sure it is set up.  Set out your FAR/AIM, charts and plotter, E6B, charts, A/FD, scratchpad and pen/pencil on the table and easy to access for the exam and flight planning.  Check your flight bag the night before and make sure you have all your needed gear - E6B, headset, etc that you will need for the ride.
That's about all the pointers I can give you, the rest is up to you.  Good luck, birdman.  Keep the pointy end forward and the dirty side down.


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What is the relationship between your tail number and air traffic control?
Obviously a tail number is used to distinguish yourself from other aircraft, but after the first call, a callsign does the same thing. It is also used for investigation purposes I would imagine, by listening to radio recordings, but are controllers typically even able to read tail numbers from the tower or do they just see a plane around where you say you are calling from and assume that it's you?

You may want to read up on how transponders work and what they are used for.

Oh they have your tail number programmed in? That would make a lot of sense, I don't know why I didn't think of that. I thought they only transmitted your squawk code.

Actually, I did look it up and while Mode C sends out your altitude of course, not much is said about tail numbers. There is a mode S, however, that could send out a transponder ID that could be paired with an n-number or an airline code.

Hi.  Welcome to Aviation.SE.  I'm confused.  If you have a call sign, you use that and do not (normally) give a tail number.  If you don't have a call sign, it is the tail number.  Why would ATC need to "read" it since you have given it to them.

Because for most of us (not airline pilots, IOW) it's probably a lot easier to remember our tail number - especially if it's our own plane - than a call sign that changes with every flight?  And how would ATC deal with generating those call signs?  OTOH, scheduled airline flights might use call signs/flight numbers because the same flight is done regularly, but possibly using a different aircraft each time.

Your title asks one thing but your question body asks another, please edit to clarify what you want to know.

@757toga no relationship to anything in ATC except that it is used as the aircraft callsign in the absence of a flight number.

Sometimes your callsign is your tail number, particularly on General Aviation flights. For example, if you are flying the Cessna 152 with tail number "N123AB", you would call ATC with "November-One-Two-Three-Alpha-Bravo".
Commercial flights, on the other hand, tend to use their flight number as the callsign. E.g. if an aircraft is operating for Delta Air Lines flight 123, the callsign would be "Delta-One-Two-Three". This is not applicable to GA as GA do not usually fly a particular route or for a particular company. Assigning a flight number to every GA flight would be troublesome, it is simpler to just use your tail number as it is guaranteed to be unique.
Controllers may identify a plane by tail number when you are on the ground, but once in the air it is almost impossible to sight a plane this way. If this is your initial call to the controller, you would describe your location, which allows the controller to identify you on the radar screen. If the controller is unsure, you may be assigned a squawk code and even asked to push the IDENT button. You may also describe your type to the controller, like:

"Tower, N123AB is Cessna 152, 5 miles South of XYZ, (...)"

You are correct that if you do lie about your callsign, ATC as no way of knowing it unless somebody sees you, as described in the "Inside Air Force One" documentary by National Geographic when they tried to pretend to be a GulfStream aircraft to secretly transport the president. If you have ADS-B installed ATC will be able to see your callsign as it was programmed into the ADS-B unit, but even that can be re-programmed.

Do you have any more info or links about the documentary you mentioned? Sounds interesting!

@Notts90 the documentary is copyrighted, but a brief search on the internet should get you a copy.

Is there a specific situation where you do or don't preface your tail number with an aircraft type? I've heard it done both ways

@TomMcW Depends. I once heard of a controller mistook an airplane for a helicopter and instructed that guy to land on a taxiway. In your home field you probably don't have to do that, once they hear "Alpha-Bravo" they know it's you.

@kevin It wasn't Harrison Ford was it? He flies helicopters too :D

@Notts90 - Was it this one (IMDB link)?

@TomMcW Substituting the type for country prefix (November in the US) is optional, but it lets ATC know what performance you're capable of, which in turn can also imply what level of pilot skill they can expect.  It's also helpful for other pilots to know whether they have the right plane in sight; we can't read tail numbers from a mile or two away, but we can (usually) see high/low wing, single/twin/jet, etc.

@TomMcW LOL, no, it was just some regular guy.

Air Traffic Control primarily provides aircraft separation services to aircraft  operating under Instrument Flight Rules (IFR).  In US airspace, aircraft operating in US airspace under Visual Flight Rules (VFR), flying in and out of un-towered airports are not necessarily required to identify themselves to ATC.  VFR traffic does not receive ATC separation services, they are expected to see and avoid other aircraft and obstacles.
ATC will know the registration number of all aircraft they provide IFR separation services to from the IFR flight plan. The radio call sign may be the aircraft registration or the Flight ID (in the case of an airline).
In order to provide efficient and safe use of the airspace for IFR traffic, ATC does employ various aircraft surveillance systems. One of those systems relies on onboard Mode S Transponders.  The S stands for selective or addressable.
Every aircraft registration number (World Wide) can be translated to a unique ICAO 24 bit address. If an aircraft is equipped with a Mode S Transponder, every transmission of that transponder will contain the 24 bit ICAO address that maps to the aircraft registration.  General formats for the ICAO 24 bit address are defined in ICAO Annex 10 Volume 3, Chapter 9.

Mostly, it's used for billing and resolving disputes.
We also use it for incident reporting, as you mentioned.

Who do you mean when you say "we"?

Check out the image on the bottom of this page: http://www.oocities.org/rjt02/behind.htm . For a general aviation aircraft (as the above poster described), when you contact a controller from the air, you'll tell him what you are (Cessna Skyhawk), who you are (N123AB), where you are (5 miles south east of XYZ airport at 6,000 feet), and what you want (inbound to land at XYZ (or) requesting flight following to JKL airport (or) transitional your airspace (or) requesting Bravo clearance etc).
The controller will look on his radar, which shows not only the position of aircraft, but also the altitude and squawk code. When you tell him the tail number and type, he can edit that blip to add that information.
Callsigns are useful for a few situations. First of all, the controller will know instantly that Delta 1234 is heavy and fast. Similarly, they can identify some special operations by name (SAR missions, military aircraft, police helicopters, skydive ops).
It's not plausible to give every aircraft its own callsign, but for aircraft that a controller interacts with frequently, and operate differently from the norm, it's another tool allow ATC to manage mental workload.

Your tail number is your callsign, if you don't have another one to use.

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Do airlines have an ATC schedule they have to adhere to?
Do airlines have to include a departure window when they file their flight plan, or communicate it otherwise?
As many people know, airlines operate on schedules, but I think we all have seen delayed flights, sometimes for 10 mins, sometimes for a couple of hours. However, that is the airline and the customer's problem. Do ATC or the Management at the airport have a departure window though, so if the plane does not depart in between these times; and it is not the airport's fault, they will not let the plane depart, or fine them?

Yes, they do have departure windows, but it is more for airspace congestion than the airport trying to get them off the pavement. Sometimes the destination airport may be the cause of the delay, outside the control of the originating airport or ATC.

The estimated off block time, EOBT, which is the time at which the flight is planned to leave the gate at the departure airport, has a validity of +/-15 minutes. If the plane is not able to depart within this window, the company must send a new ATC flightplan with an updated EOBT.
In some cases a calculated takeoff time, CTOT, is issued to a flight. This is the exact time the plane must begin its takeoff roll. It is given based on airspace or airport congestion along the planned route of the flight, to prevent overload in individual ATC sectors. The flight must begin its takeoff roll within -5/+10 minutes of the CTOT. If unable to comply, a new CTOT must be requested.

Here is a data point: about a month ago I flew AJA-CDG. We boarded on time, door was closed, and then the captain proceeded to tell us that we had to wait one hour and forty minutes for take off.
Because of storms, traffic in Paris was backlogged, and to request their slot they needed the plane to be ready for takeoff. Only then they were able to make their request to traffic control.

This should be a comment, not an answer, it doesn't provide any kind of evidence to the OP's question, just a personal experience as a passenger.

It is evidence, unless you are calling me a liar.

Still doesn't mean it is an actual answer, it provides nothing that the OP is asking.

The question is "Do airlines have an ATC schedule they have to adhere to?", and I'm providing a concrete example that they do.

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The nav accuracy during SID and STAR
Does anybody knows is there any document where is described the nav accuracy during STAR and SID? I mean, how far can I deviate from the path as much as possible?

TSO-c129 define the requirements for non-WAAS GPS receivers.  In these receivers, TERMINAL (T) mode is equivalent to RNAV 1 and extends from the departure and destination 30NM.
Between those two airports, ENROUTE mode is activated (> 30 NM from departure or destination airport).  ENROUTE mode is equivalent to RNAV 2 procedures.
APPROACH mode starts at the capture fix and on these non-WAAS receivers, it is equivalent to RNAV 0.3 mode.

SIDs and STARs are RNAV 1 requirements.  This means the receiver needs to have a 95% confidence that it knows where you are with 1NM of where you actually are.  Also, full scale deflection of the GPS needle is 1NM.
Enroute structures like Victor and Jet airways, and Q and T routes are RNAV 2 procedures and the receiver needs to know where you are within 2NM just like the previous example.
As another answer pointed out, SIDs and STARs can extend greater than 30NM from the departure or destination airports, but they are still RNAV 1 procedures.  The crew must be aware and monitor "actual navigational performance" to ensure it meets RNAV 1 criteria.

TSO-c146 WAAS GPS receivers account for the distance on SIDs and STARs and will stay in TERMINAL mode (RNAV 1) until the end of the SiD or the beginning of the arrival.

AC 90-100A change 2 describes this pretty well

(5) The navigation standard (for example, RNAV 1 or RNAV 2) required for all RNAV
procedures/routes will be clearly designated on all appropriate charts. However, SIDs, ODPs,
and STARs will be flown with RNAV 1 procedures. (page 6)

On RNAV SIDs and STARs, the plate will typically remind the pilot of the RNAV RNP.

For non-RNAV SIDs and STARs, the airway extends 4NM from the centerline until 4.5° radial change intercepts the 4NM area at 51NM.  At that point, the airway obstacle clearance expands at 4.5°.
FAA TERPS Order 8260.3F

This is an interesting question, because the FAA docs, like many large complex organizations, often have vague or contradicting definitions.
RNP APPR, the navigational precision required for final approaches, narrows starting at 1 NM from the runway, down to .1 NM near the runway.
RNP 1 (full CDI deflection is 1NM either side of the course) is required for “arrival and departure in the terminal area, and the initial and intermediate approach phase.”
RNP 2 (full CDI deflection is 2NM either side of the course) is required for enroute operations in the US.
(It’s worth noting that there several technical criteria that define RNP 1 or 2, and the CDI sensitivity is merely the visible indication to you as the pilot, there’s a lot more to it.)
The problem is that the definition of a SID or STAR’s normal lateral dimensions don’t exist.  A large arrival could start hundreds of miles from the runway.  Does this constitute the “arrival and departure in the terminal area” that points to RNP 1?  Probably not.
The FAA defines the “Terminal Area” as “A general term used to describe airspace in which approach control service or airport traffic control service is provided.”  By that definition, you would switch from RNP 2 to RNP 1 when you leave the ARTCC sector and enter into the approach controller’s sector.  That line may be very clear to the controllers, but will be very vague to the pilot.
So you are actually flying the inner 20-30NM of the SID or STAR under RNP 1, and the outer part under RNP 2.

Where are you getting these definitions for navigation specifications? There are many errors in this response, starting with the first one listed. RNP APCH has, as a total system error, a 1 NM for many segments but is down to 0.30 NM for the final approach segment. Meanwhile, US RNAV DPs and STARs require RNAV1, not RNP1. Likewise, enroute RNAV requires RNAV2.

@Timbo Information comes directly from the AIM, see Chapter 1, Sections 2…  Specifically 1-2-1-b-2-E.  And then really all of 1-2-2, with special focus on Table 1-2-1, and paragraphs 1-2-2-b-1-a.

Thanks for your answer!

@MaxR, thanks… though you have misrepresented RNP APCH as RNP APPR. Likewise, RNP 1 is NOT required in the US for arrival and departure. RNAV1 would be the correct NavSpec for an RNAV procedure. Finally, RNP 2 is NOT required in the US for the enroute phase. I believe you’re just misquoting the AIM.

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Can we use leaf shutter mechanism as a drone dropping mechansim for payload weight of 3lbs?
I'm considering implementing a drone payload drop mechanism capable of handling payloads weighing up to 3lbs. I'm intrigued by the idea of using a leaf shutter mechanism for this purpose, but I haven't found any existing examples online. Before proceeding, I'd like to ascertain the feasibility of this approach for our drone project. Additionally, I'm interested in understanding the potential advantages and disadvantages of incorporating a leaf shutter mechanism into our drone design.

Should be migrated to Drones stack exchange unless "do my project for me" is off topic there

No.  Leaf shutters are designed for speed, not for supporting mechanical loads.
Instead, just put a loop on the top of the payload.  Put a pin through the loop.  Retract the pin, in your case with a cheap tiny servo.  Then the payload falls.  Simpler, more reliable, secures the payload before release, fewer parts to fail or maintain, less friction, much heavier payloads possible, and it's been used for decades -- maybe centuries if you count dropping things from kites.


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What are the maximum dimensions and weight per piece that can be loaded on a 737-800BCF (Boeng Converted Freighter)
The 737-800 Boeing Converted Freighter aircraft cargo specs are widely available on the Boeing and other related websites, but the actual per piece maximum dimensions and weight than can be fitted on a 737-800BCF are the subject of the question here.


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Could a VTOL aircraft use a helipad for landing/taking off?
In more recent years, VTOL (Vertical Take-Off & Landing) aircraft have become fairly popular and are used in some notable air forces (such as the USA and the UK). I was wondering if these aircraft could land on something like the helipad many big boats like cruise ships have or even rooftop helipads like what many hospitals have.

1969 is a broad definition of "more recent years" :-D The UK introduced the Harrier before Neil Armstrong stepped on the Moon.

There's barely a hundred F-35B's operational... way down from 278 Harriers and 232 Yaks at the 1980s heyday of VTOLs.

Also a 'notable navy', I think?

Not necessarily
The two key elements are aircraft mass, and how that mass is kept aloft.
You can probably get a Chinook onto the landing pad of a cruise liner, but you would want to check first if the structural supports under it can take the 10+ tonnes rather than the 1 tonne jet ranger it was probably designed for.
Helicopters support themselves by moving air through the rotor disk down, so larger helicopters produce more air movement which may cause damage to surrounding fixtures.
This is relevant for VTOL aircraft since those using propellers like the V-22 Osprey are normally running smaller disk areas at higher velocities, being more likely to damage nearby structures. Worse are jets like the Harrier or F-35 which are heavy (10-20 tonnes) and supported by quite narrow cross sections of air at very high velocity - for the aft stream this is very hot engine exhaust likely to melt or burn plastic or wood surfaces.
One of the early Harrier pilots notes doing an early public demo where intended landing area had been covered in metal planking but during approach a channel was carved into the grass by the airflow, that then caused parts of the planking to lift.
There may also be issues with the more restricted control authority of a VTOL aircraft in hover compared to a helicopter in dealing with turbulence or other effects of nearby structures, along with worse visibility downwards.
In an emergency you can probably land a VTOL aircraft onto an standard helicopter pad (especially if doing so because low fuel eg lighter), but before doing so regularly some non trivial re-engineering would be wise. Noise may also impact feasibility of regular use.
And certainly there will be marginal areas for helicopter landings (eg soft surfaces or enclosed trees) that would not be possible in a VTOL aircraft that you want to fly again.

Harriers cool their exhaust with water, so are less damaging than you would expect.

As a concrete example, https://news.usni.org/2016/03/22/uss-america-back-to-sea-after-completing-10-months-of-deck-strengthening-for-f-35s; "The aviation-centric big deck was commissioned in late 2014 but required additional work to take the day-to-day strain of operating the short takeoff and vertical landing (STOVL) strike fighters that will operate from the ship."

for another concrete example of how it can go wrong, see this example where a USAF Osprey taking off destroyed the helipad at an English hospital: https://www.cambridge-news.co.uk/news/cambridge-news/addenbrookes-hospital-helipad-damage-helicopter-20444102

@Tristan You beat me to it! I was here to post the video: https://www.youtube.com/watch?v=vSDMzeIOb-8 Strictly speaking, the question asks "Can it land...?" And really in this particular case, the answer is "Yes, although only the one time!"

You mention air forces but don't specifically restrict the question to current military types, so considering commercial VTOL aircraft this is exactly what Joby and other air taxi companies are planning. These could be employed by the military, though I don't know of any plans.


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How do you stay stable when landing / taking off an F-35 during a VTOL landing/takeoff?
I saw a video of a F-35 landing vertically using its fans and was curious as to how they do that without a tail rotor? Why don't they spin out like a helicopter does when it loses its tail?

Wikipedia says the lift fan of the F-35 is contra-rotating

@bergi I didn't know that.  here is a link to a Rolls website saying so https://www.rolls-royce.com/products-and-services/defence/aerospace/combat-jets/rolls-royce-liftsystem.aspx

Slightly related, and an excellent article, especially if you have controls in your background: https://flyingv.ucsd.edu/krstic/teaching/143b/GSBode.pdf

The tail rotor of a helicopter is primarily there to counteract the torque of the main rotor.
The F-35's lift fan is counter-rotating such that it cancels its own torque.  In addition to the lift fan, lift and control is provided by the engine exhaust nozzle at the tail as well as two roll posts off the side of the engine.
It is interesting to compare a video of a Harrier in hover to an F-35.  The Harrier was manually controlled, the human is constantly adjusting the controls to maintain a hover.  Consequently, the Harrier seems to wiggle around -- like balancing on top of a ball.
The F-35 is fully fly by wire under digital closed loop control.  Its hover is rock-steady.  Rather than the pilot directly controlling the thrust vector angle or control surface deflections or any other control effector -- the F-35's pilot's controls express intent.  Go forward, go back, go up/down, go left/right.  The computer figures out how to make that happen.

The F-35-B STOVL variant of the Lockheed-Martin F-35 Lightning II gets its V/STOL / STOVL capabilities from the Rolls-Royce LiftSystem, which consists of four main components:

The Three Bearing Swivel Module (3BSM), which allows to turn the nozzle downwards 90° in order to act as a vertical lift system.
The two roll posts on the wings, which divert bypass air from the turbofan engine in order to provide roll control during hover.
The 29000 hp driveshaft and clutch, which allow diverting power from the turbine to the …
Rolls-Royce LiftFan, a pair of contra-rotating fans providing lift forward of the center of gravity to counterbalance the lift generated at the aft.

The important aspect for this question is that the two fans of the LiftFan are contra-rotating, i.e., spinning in opposite directions. Therefore, just like any helicopter with contra-rotating (e.g. Kamov Ka-27 or the most famous of them all, NASA JPL's Ingenuity Mars Helicopter) or counter-rotating (e.g., Boeing CH-47 Chinook, Kaman K-MAX, Bell Boeing V-22 Osprey) rotors, the net torque between them is zero, ergo, there is no need to cancel out the torque using a tail rotor.

The contra-rotating liftfan that creates no torque is the answer to the question.
But if you're wondering how to yaw the aircraft, the F-35B has a three bearing swivel duct (3BSD) providing the aft post of thrust and is capable of vectoring thrust not only in pitch but also in yaw, with a yaw angle of -/+ 12 deg.
The following figure shows all the four Propulsion Control Effectors, and their deflection angles:

Now regarding how to stay stable in a VTOL process, the control allocation of those effectors are provided by the Incremental Nonlinear Dynamic Inversion Control Law (INDI CLAW). As distinguished from legacy FBW schemes, which use preprogrammed (scheduled) gains, the NDI/INDI approach allows the aircraft to determine a control solution on the fly, based on a detailed onboard flight dynamics model (OBM) of the aircraft’s thrust profile, mass properties and aerodynamic data such as stability and controllability derivatives.
In short, the regulator and command modules implement the desired dynamics for the pilot controlled axes (pitch, roll, yaw, height, and axial). The effector blender allocates desired acceleration commands optimally to the control effectors (e.g. propulsion posts and conventional control surfaces), best suited for the particular axis.


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What is the use of this remove before flight cover on the nose of a Bombardier Global 6000?
I recently saw a Bombardier Global 6000 at my local airport. I was just wondering what the use of this circled remove before flight cover on the nose of the Bombardier Global 6000 is. I never saw such covers before on a aircraft. What is the cover covering and why are the 3 ones connected with a wire?

(Own work)

I hope you don't mind, I shamelessly lifted your photo for another question.

No problem if you mention the source.

I did. Nice photo BTW

Here is the jetphotos.net url: http://www.jetphotos.net/photo/8417782

yes I would like this too

My question was: What's under the circled remove before flight cover and why are they 3 remove bevore flight strips connected with a wire?

I know what this things are. I just want to know the circled things.

I've edited the question

These covers are used to keep foreign objects away and out of the air data sensors, pitot tubes, static ports and Angle of Attack sensors (large red covers) while the aircraft is resting on the ground.  Blockage or damage to these sensors by foreign objects prevents the aircraft flight control computers and instruments from collecting accurate data and could be disastrous in flight, especially in instrument conditions.  The wires are essentially a leash to hold the neoprene covers together in a group and both prevent their loss during storage and ensure that all covers are removed from the sensors during pre-flight.

I know the use of remove before flight covers but the question refers to the big one in the middle and why are they connected with a wire? I've just edited the question.

I've just added the circles to the image.

In my opinion, the pitot tubes are right underneath the circle. It looks way to big for pitot tubes from my point of view.

Those are heated AOA sensors

And they are covered like this, that nobody can move them?

No just to preven them from being bumped into or damaged during ground towing, hangaring, etc.

@PascalAckermann To learn what can happen if you don't cover these, see Birgenair Flight 301.

Better yet, XL Airways flight 888T


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Where can I get a picture of a specific aircraft by registration?
I'm actually building a website where I want to display pictures of a specific aircraft. So I have the registration and I would like to show a picture next to each registration. For example I have the registration: A7-BCW
I want to get the picture in a way like this:
website.com/a7-bcw.jpg

Is there any site where I can do this and where I'm allowed to use the pictures for my site (watermarks are OK and I would also display the copyright information)? Of course there is no site where I can look up every aircraft around the world, I just need it for the common airlines like Qatar, Emirates, Singapore Airlines, Delta, United and so on.

I suggest you send an email to the major aviation photo sites out there (airliners.net, jetphotos.net etc.). That will give you a much better answer then you will get here.

Use flightaware.com.
They don't have every plane, but people can upload photos for a registration.
For example:
I search N6525W, and this page comes up.  Then I can click the thumbnail picture of the plane in the top left section of the main body and I get this big picture.
Go there, and if you're lucky, the plane you're looking for happens to have a photo.

I notice that you're needing this for web development in bulk.  You need to make sure you're not stealing photos.  Ask for permission first.

Pictures appear to be require self uploading.  I have not uploaded any of my plane there, nor are there any Fixed Gear (FG) pictures of my airplane type loaded, only Retractable Gear (RG). flightaware.com is not very current for the flights it shows.  I found a flight I did in February 2018 for a transponder checkout, where we did not talk to ATC. No subsequent flights, including several where we did talk to ATC, are shown.


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What does the ATC term "a company traffic" mean?
During my flight training I often heard the term "a company traffic" in radio calls from the ATC like:
N123AB a company traffic is joining downwind runway 24

What does "a company traffic" mean? Why not just mentioning the type of the aircraft like:
N123AB traffic a Piper Archer is joining downwind runway 24

Note: I'm flying in Europe (Switzerland), so maybe it's only used by ATC in my area.

Having listened to some live ATC (feeds from US-based airports) I've always heard that as "a company aircraft" which I assumed to mean an aircraft from the same airline (with the same paintjob).

Okay that would make more sense to me, so I'll change the question.

Additionally, what I've heard/understood of ATC (admittedly very little, as I'm not a pilot nor in training), is that it is "company traffic", not "a company traffic". Of course, that could be due to listening to native English speaking controllers in the US vs multi-lingual controllers in the EU.

@ratchetfreak based on everything I've learned here, that would be the answer. You'll get more magical internet points that you can redeem for rainbows and unicorns if you'll post that as an answer...

It means that the traffic to watch out for is from the same airline (and with the same paintjob) as the aircraft ATC is talking to.
Most twinjet airliners look alike from a distance so using the paint job to differentiate them at a glance is preferable over the type.
Using "company" instead of the actual company name makes it clear that there is at least one other aircraft with that paintjob instead of potentially being the same aircraft. (this confusion is more likely when the monitoring system doesn't have full coverage).

Same type is possible but I also heard it across different types. But always for aircrafts from the same flight school.

"company" means having the same operator, which is obvious to ATC if they have the same callsign, e.g. airlines, scheduled cargo, charter, etc. I've even got it a few times for other planes from my flight school, despite not having a callsign, because Tower knew our tail numbers.

The last part of this is the most important IMO - it reduces potential confusion: If you're a Delta 737 and ATC tells you "Give way to the KLM and the Delta 737 from the right, then proceed", you could potentially get confused and think you ARE the Delta aircraft being referred to and ATC has gotten confused. Whereas "Give way to the KLM 737 and company 737 from the right" makes it clear that there is another aircraft.

Paint job is not known to Enroute controllers, it just means from same airline. Also some airlines put out special paint jobs with the controller having no idea. The main reason some controllers tell them ‘company’ is so if they communicate with each other they use a company frequency.


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What aspect ratio is best for Wind Tunnel Testing an aerofoil with Small Additives?
Vortex generators will be 3D printed on a panel, which is then to be slotted onto a foam aerofoil to be tested in the wind tunnel for performance and flow physics.
What I want to know is which aspect ratio to use?
Rectangular wing, need a chord length and span.
Max wing span is 700mm.

What is it you want to test?
Do you want to test the 2D characteristics of an airfoil? Then make it the width of the windtunnel. The wind tunnel walls act like mirrors, so you will have the behaviour of an infinite wing.
If you want to test a 3D wing on a model, you need to use coherent scale. Use the same scale for the fuselage/wing/empennage.


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Range, Endurance and Fuel Cost Savings of an Aircraft
I have recently carried out CFD simulations on the A320 fuselage and modified its fuselage.  I did this by matching the Reynold's number of the cruising altitude. The reference values were taken at the sea level conditions, v = 90.10m/s, density 1.225kg/m3 etc. I found out that the Cl and Cd values were -0.00136 and Cd value is 0.0340 with a cross sectional front profile area of 12.83m2. For the modified fuselage, the cross sectional area is 13.53m2, Cd is0.0314 and Cl is -0.0091.
I would like to calculate the Range, Endurance and Fuel cost savings due to the modified design.  How can I do this?

With only one point and only the isolated fuselage is a bit difficult to make a comparison... You need at least 3 point and the whole airplane to built the polar and then you can compare it with the official one

At a minimum, you need to vary alpha to match lift at the same flight condition and then compare the drag coefficients.
Comparing drag at different lift is meaningless.
Both analyses should be performed at a cruise condition -- not sea level, and such that Lift = Weight.  Your negative CL makes this very unlikely.


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How can I find the minimum and maximum airspeeds for efficiency with a specific prop/engine combination?
I'm operating a Cessna 180 with various wing and weight mods with a TCM IO550D engine and a McCauley Black Mac (D3A34C401/90DFA-2 3 blade (88 inch) seaplane prop. I operate Lean of Peak (LOP) for most ops, and accept some airspeed loss for the benefits of LOP. At some point of loss of airspeed, the resultant inefficiency of the power plant is counter to any fuel efficiency gained by LOP. I'm trying to understand where this airspeed intersects, at a given altitude.
A second part of the question, is what factors affect efficiency loss at top power settings in both cruise and for takeoff? For example, continuous, unlimited full rated 300 Hp is only available at WOT and 2700 RPM, but it is insufferably loud at that RPM. McCauley indicates the prop's max pull is at 2600 RPM. What am I gaining or losing by taking off, or flying with 2600 RPM vs 2700 RPM? Is there a useful chart for evaluating engine/prop combinations?

The POH is not useful due to the many mods on this plane, including the engine and prop STCs. Nor does it account for LOP operations, though I have good data through an engine monitor. Max propeller efficiency for my prop before the tips go supersonic is determined by P-Ponk to be 2600 RPM as it was included in a series of efficiency tests with various engine combinations. However, P-Ponk did not issue this STC - Air Plaines did.

For practical purposes, I plan to record max and min airspeeds at 2000' increments up to 12,000, and the hp necessary to achieve it. Then I'll work out the various ROP and LOP fuel and RPM combinations to obtain that performance and be able to calculate new range and speed charts. The overlapping mods do not account for this kind of data.

max and min cruise airspeeds in the comment above.

If you do have a variable pitch prop, higher efficiency will (of course) be found a subsonic prop speed and higher pitch.  If you can stand the noise, climb rates could be tested at 2600 and 2700 rpm, but vibrations caused by trans sonic prop speeds would be a major concern.  Expert advice would be in order.

You may want to read this paper and examine how Norris and Bauer completed a flight performance assessment of a Luscombe 8E.  The Luscombe would be an approximate 7/8 scale 180, just considering the comparison, generally.  Their evaluation could serve as a guide for completing a similar assessment for your 180.  The paper was originally referenced in an answer by Peter Kämpf, here.

What am I gaining or losing by taking off, or flying with 2600 RPM vs 2700 RPM?

Something you might want to consider on launch is propeller stall.  Propeller whirl tests to determine thrust are accomplished on a static thrust dynamometer.  Consequently, the maximum thrust at a specific rpm given by the manufacturer will be static thrust.  The loss of thrust at a yet higher rpm could be due to the initial onset of propeller stall, or otherwise balancing in the constant speed adjustment to reduce blade angle of attack, resulting in a slight loss of blade lift, or thrust.  Once in level flight approaching cruise, however, propeller stall or an otherwise reduction in thrust, under these mentioned rpm conditions, would not be foreseen as an issue.
You mention the sound is insufferably loud at 2700 rpm.  This could be due to the propeller tip velocity exceeding the speed of sound.  Just as this occurs, there is a slight but noticeable drop in propeller efficiency evidenced by a loss of thrust.  Do the calculations suggested by Niels Nielson to determine the tip velocity of the propeller vs rpm.  Keep in mind that in flight, the vector sum of airspeed and prop rotational tip speed determines when the prop tip will exceed the speed of sound.
As you have indicated you are operating your plane with various wing and weight modifications, you may have to assess the flight performance of your plane by using PIW or VIW methods.  The acronyms stand for power independent of weight and velocity independent of weight.  These methods are used to back-figure various aspects of flight performance by application of relatively simple aerodynamic equations for thrust, and related factors. You may want to read this paper by Connick regarding flight testing and assessment of the performance of a Piper J4A Cub Coupe. Their assessment provides an excellent example of the process in determining flight performance factors similar to those of your interest. As a place to start, which will not cost anything, you can investigate the application of these methods using data from your POH or that for any comparable aircraft. The most important aspects are related to power required vs power available.  All other factors (or most of them) can be derived from these. Rob McDonald has given you an excellent start regarding your power plant.  An assessment of your propeller will determine the useable (available) power. Here is an extract of an ongoing similar POH approach estimating factors for other Cessna aircraft.
Added in edit - As additional information regarding propeller analysis, David F Rogers of NAR Associates has provided several papers available at NAR-Associates.com, which discuss aspects of propeller efficiency for different flight conditions such as takeoff, climb, and cruise.  These papers are quite insightful in the examination methods for propeller evaluation.

What you really need to do this analysis is a detailed propeller map and a detailed engine map.  Then you can do some analysis to match them together and make your own combined map.
Piston engine maps are often included in POH or other aircraft documentation, you can probably find one for your IO550D fairly easily.
Prop maps are much harder to come by.  However, you may be able to obtain one by contacting the company.
Although I use the word Map -- implying a piece of paper with a chart on it, it could also be provided as a table of numbers -- or these days as a computer program that performs interpolation between points of an internal table of data.
Edit to discuss chart linked to by OP in comments.

This is a simplified performance chart for this engine -- the important thing about this chart (that is not explicitly stated) is that it is for performance with a (particular) fixed pitch prop attached.
A different style of presentation would be used with a constant speed prop.
At the top of the page, the altitude is specified.  This chart is also for a specific airspeed -- but unfortunately, that is not indicated anywhere I can see on this page.
The bottom two curves use the vertical scale at the lower left for BSFC.  The middle two curves use the scale at the right for BHP.  The top two curves use the scale at the upper left for manifold pressure.
All of these quantities are plotted as a function of RPM (the x-axis).
There are two curves because one represents the engine's performance at full throttle.  The other represents the engine's performance with a fixed pitch propeller attached (at sea level and a particular airspeed).
The full throttle line represents the maximum operating capability of the engine -- in this case, it looks like it is mainly operating at about 29 inHg MP.  If it were attached to a brake in a dynamometer, these are what the power and fuel flow curves would look like as RPM is varied.
However, the chosen fixed pitch propeller can't absorb 240 Hp at 2200 rpm.  Instead, at 2200 rpm, it only absorbs 160 Hp with the engine at 23 inHg.
If the pilot advances the throttle (say to 200 Hp), the engine will produce more power than the prop can absorb, so there will be an excess torque applied to the shaft, and the propeller will accelerate to a faster rpm -- until 2350 rpm.
The prop is the load applied to the shaft -- the engine is the thing trying to drive the shaft.  They must always match RPM (or the shaft is broken).  The torque in and out must also balance -- knowing that you can accelerate / decelerate when out of balance.  Just like with forces.
For a propeller, we have the advance ratio $J$, it is a function of the true airspeed ($V$), the engine speed ($n$) (in revolutions per time, not radians per time), and the propeller diameter ($D$).
$$J=V/(n\,D)$$
In many ways, the advance ratio is like the angle of attack of a wing.
For a fixed pitch prop, the power coefficient is a function of the advance ratio.  This is like saying the drag coefficient is a function of the angle of attack.
$$C_P=f(J)$$
There is also a thrust coefficient -- but I'm ignoring that for now.  The thrust coefficient would be like the lift coefficient in this analogy.
For a variable pitch prop, the power coefficient is also a function of the blade angle.  But this chart is for a fixed pitch prop.
$$C_P=f(J, \beta)$$
The power coefficient is dimensionalized to shaft power like this
$$P_{shaft}=C_P\,\rho\,n^3\,D^5$$
This is entirely analogous to dimensionalizing the drag from the drag coefficient like this
$$D=C_D\,0.5\,\rho\,V^2\,S_{ref}$$
So, in this chart, propeller performance is for a fixed pitch prop at a single altitude (i.e. density $\rho$), and a single airspeed ($V$).
Starting at low throttle (2000 rpm), we are at some $J$, which means a particular power coefficient $C_P$, which is then dimensionalized to our $P_{shaft}=120$Hp.
Advancing the throttle, each point is for a different advance ratio $J$, which means a different power coefficient, and a different shaft power.
If we were to change the airspeed (say faster), the advance ratio would change (increase) at a given RPM, so the $C_P$ would change (decrease - I haven't shown a $C_P vs. J$, but trust me).  And so the power absorbed by the prop would decrease.  Since the pilot did not change the throttle, the engine's output power now exceeds the propeller's absorbed power and the prop will accelerate -- we've put the airplane in a dive and may over-speed the prop.
A different airspeed would be represented by a different set of prop load curves.
Likewise for a different altitude, or a different propeller.

Thank you. I've reached out to Air Plaines, whose STC covers this modified engine, prop and install, but have not heard back. I do have the power performance charts for the factory TCM IO550, which I'm trying to understand, but no additional info on this prop combination.

Feel free to ask questions about the engine performance charts while you wait to hear back about the prop.  Here is a nice article in KitPlanes about how to use the standard form that engine charts are provided in. https://www.kitplanes.com/determining-engine-power/  There will be an additional chart that covers fuel flow.

For clarification, by no additional info, I mean Air Plaines, whose STC covers this prop install on their engine, does not publish any changes to performance for the prop install. The STC states, "All parameters of Basic Flight Manual Charts will vary. Take off and climb performance will be improved. Cruise performance NOT evaluated."

Here is a chart I'd like to understand. I can't add a photo, but believe the link is direct to the chart. https://www.manualslib.com/manual/1595758/Teledyne-Continental-Motors-Sandcast-Series.html?page=113#manual

I am still not clear on why this chart is defined by a fix pitch prop - is that simply isolating engine hp performance from the prop/engine like a dynamometer? The kitplane article was very helpful in explaining how to read the most relevant chart.

If this chart was for a constant speed prop, the load line would be a vertical line -- i.e. at constant speed.  The constant speed governor varies the load (by changing pitch) to equilibrate the torque and maintain a constant speed.  So, you can vary from low part power to max throttle and the load line is a vertical line.

Here is a minor addition which might help a little.
Knowing the prop diameter and the speed of sound, you can calculate the shaft RPM at which the prop tips go supersonic. When that happens (or actually a little before) the thrust flattens off and the noise generation goes way, way up- and the propulsive efficiency of the prop goes down. That is, you burn more avgas but you do not get more performance. This is probably the difference between 2600 and 2700 RPM in your example.
One simple way to demonstrate this would be to affix a stout spring gauge or load cell to the end of the fuselage, tie off the other end to something heavy, power up and measure the tension force (thrust) as a function of RPM with the prop set to fine pitch between 2500 and 2700 RPM.
Or alternatively, just wait for Peter Kaempf to get out of bed (mind the time zone difference!) and furnish his answer!

Thanks! P-Ponk did that analysis on many props, including mine, concluding that across most of these, including my model/length, 2600 is the magic speed. We always pull back, accordingly because we love aviation and our neighbors, but this noise profile is well known and most powerplant experts from Continental to McCauley to GAMI and APS still recommend full rated power. So this leads me to wonder what's to gain by 2700 RPM? Is it simply the burst of thrust from static that helps my float plane get on step quicker, or does that loss of efficiency above 2600 offer no performance benefit?

@DustyFlier, here's the deal... the speed of sound depends on density altitude which will vary all over the place, and while the tips exceed mach 1, the shanks of the blades are still producing thrust. That's what is probably to gain by 2700 instead of 2600. the spring gauge test will yield the correct answer... -NN


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Does a helicopter actually have a lower rate of fuel consumption in cruise than in hover?
Recently the thought of autogyro flight as "powered autorotation" came to mind.  The rotor acts like a fixed wing, providing lift, while a separate source of thrust provides forward motion.
A helicopter tilts its rotor forward a bit using for both lift and thrust.
But once it moves forward, it would seem the change in relative wind through the rotor may improve its lifting efficiency.  But, as with fixed wing aircraft, forward motion increases form drag.
What does a helicopter pilot do with the controls when the helicopter accelerates to cruise?  How does the rate of fuel consumption change?

The power required diminishes from hover till a speed known as $V_y$ and then rises again till $V_{ne}$, a bit like an airplane.

That diminishing of power till $V_y$ is because in hover, the helicopter flies it its own downwash, whereas in forward flight, this phenomenon is largely reduced. This downwash in hover causes induced drag on rotor blades, and requires more power from engine for the same amount of upward thrust. Beyond $V_y$, the parasite drag takes over ("ahead of the power curve") and so the power required increases. Also, at higher speeds, the functionality of the tail rotor is virtually replaced by the more efficient vertical stabilizer, which further improves the efficiency.

@AdityaSharma you might want to make a proper answer out of that, probably with some diagrams & graphs, ideally with measured values from the real world :)

You cruise an R-22 at about 90-95% of max power, Max Continuous, so if you are very light and say only 80-90% is required to hover in ground effect, the fuel burn in max cruise would actually be higher if you want to cruise at max cruise speed.

Does this answer your question?


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At what angle to the ground track does wind become favorable to lower fuel consumption?
We can all agree, flying from point A to B, a headwind will increase fuel consumption, and a tail wind will reduce it.  The "jet stream" inspires these types of thoughts.
Quartering headwind, crabbing into, still more fuel, right?
Quartering tailwind, probably less, but the aircraft still must oppose the cross wind component with some force which is ultimately derived from burning fuel.
Perhaps, from someone with airliner experience, at what point off my tail does wind stop assisting in fuel economy?
With the tail as 0 degrees, nose as 180, and beam as 90, my guess would be around 80 degrees, a cross wind with a bit of tailwind component.
Is there evidence from practical experience to support or refute this guess?

Comments are not for extended discussion; this conversation has been moved to chat.

To solve this problem, let's look at the vector diagram of TAS, GS and Wind Speed (WS):

(image source)
In this diagram, the angle between the desired course (ground track) and the wind is $\delta$ (where 0° is tailwind and 180° is headwind). The resulting wind correction angle $\theta$ can be calculated as follows:
$$ \theta = \arcsin \left( \frac{\text{WS}}{\text{TAS}} \sin\delta \right) $$
The resulting ground speed (length of vector labelled "Desired course") is then given by
$$ \text{GS} = \text{TAS} \cos\theta + \text{WS}\cos\delta $$
The following plot shows the wind correction angle and ground speed for an example of 400 KTAS and 50 kt wind speed at different angles:

We are now looking for the angle $\delta$, where the ground speed is equal to the TAS. This will typically be close to 90°, but not exactly. In the example above, this angle is at ~86.4°. When solving the equation above with GS = TAS for $\delta$, the result is:
$$ \boxed{\delta = \pm \arccos \left( \frac{\text{WS}}{2 \text{TAS}} \right)} $$
This result depends on the ratio of WS/TAS, meaning there is no single answer to the question. We can however plot this angle, where the wind has no impact on ground speed, as a function of this ratio (only positive solution plotted):

When the wind angle is less than this value, we benefit from the tailwind. When the wind angle is higher than this value, we suffer from the cross- and headwind.

If I understand this correctly the angle changes with airspeed and wind speed, so there is no one answer. If so, it could be more apparent, if I'm wrong that doesn't come out.

@GdD It only depends on the ratio, not the individual values. I highlighted that there is no single answer to the question.

Turns out MichaelH was not too far off suggesting crabbing into a crosswind does not have a major fuel penalty (1/(cos crab angle)). The "push" from behind is sin (angle off the beam).  Plugging in a more recreational 100 knots and 15 knots crosswind yields similar results.

To be clear, I was emphasizing that crabbing does not increase aerodynamic drag.  It will effect fuel consumption on a fixed distance leg due to increased or decreased distance (time) flown throughout the airmass as compared to over the ground.  Any wind component aft of relative 90/270 line helps, anything forward hurts.  The amount depends on direction and magnitude of the wind vector. Trig it out if you like…

Actually, I take back the “any” comment…. A very strong 91 degree (or possible greater) crosswind would likely require enough crabbing to effectively wipe out any minor benefit to the tailwind component.  Hmmm…. Good question.  How to calculate the breakeven point?

@MichaelHall This answer calculates the breakevent point. The last plot shows the wind angle below which you would benefit from the wind as a function of wind speed over true airspeed.

So now we know why we were never taught any one specific number in ground school-- fascinating--

@Bianfable, Yeah, after I said that I figured it might… I just need some time to digest the info; too much math before I’ve finished my first cup of coffee makes my head hurt!

@Bianfable, I suppose it would be correct to say that in any aircraft equipped with GPS groundspeed, (most) the breakeven point would simply be displayed GS and computed TAS being equal, right?  No need for trig while flying...

@MichaelHall Yes, that's correct (it doesn't have to be GPS ground speed, could be IRS based as well).

Sure, any GS.  I mentioned GPS because just about everyone has it now days... Thanks for confirming my instinct.


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Does the rotation direction of intermeshing rotors have any noticeable effect?
Consider the Kaman K-Max, which has intermeshing (side-by-side) rotors that rotate as indicated below (when viewed from above, the rotor on the right (green) rotates clockwise, the left one (red) counterclockwise). I was wondering, does this particular choice has any effect on handling or aerodynamics, or is it more or less arbitrary, and just influenced by the mechanical design?
Or in other words, if we had two identical helicopters but one with a reversed rotation: Would a pilot notice any difference between those?
Naively I would have thought that it doesn't matter at all, but I got curious and couldn't find any information on that design choice.

I was wondering, does this particular choice has any effect on handling or aerodynamics?

Yes it does and it has to do with the fact that the two rotors are tilted sideward for obvious reasons of clearance between the two rotor heads.
Seen from above, the right rotor rotates clockwise and the left rotor counterclockwise but due to the sideward tilt, the rotors rotate also when seen from the side.
To simply picture it, just imagine them as being tilted sideward not just a few degrees but a full 90°: now they can be clearly seen rotating from the side. So, because of the sideward tilt, the rotors rotate both as seen from above and from the side.
In particular, from the side they rotate with the blade going up when leaving the tail and down when approaching the nose, as can be seen in the following picture¹ (yellow arrow):

As usual with helicopters, whenever a rotor rotates in one direction then the fuselage wants to rotate in the opposite direction (action-reaction law aka Newton's third law). In our case, since the two rotors rotate with the blades going down when approaching the nose then the fuselage wants to rotate nose-up (blue arrow):

(Obviously it would have been the other way around if the rotors had rotated in the opposite direction).
Now, somehow this blue nose-up tendency of the fuselage has to be opposed and the easiest way to do it is by tilting the rotors a bit forward in order to create a horizontal force (horizontal green arrow in the next picture) which generates a pitching-down moment in respect to the CG. Then, the thrust of the rotors not only lifts the helicopter (vertical green arrow) but produces also a pitching-down moment compensating the blue arrow:

Why are all those arrows good when pointing like that and not the other way around? Because this increases the longitudinal stability of the helicopter: let's suppose that the helicopter is invested by a vertical upgust. This upgust pushes the helicopter upward and increases the AoA of the rotors therefore increasing its thrust as well. In this condition a helicopter is stable if it reacts against these effects i.e. if it reacts pitching-down. And this is exactly what happen when all the arrows are how they are: the gust increases the thrust which increases the horizontal green arrow which increases its pitching-down moment opposing the gust and stabilising the helicopter longitudinally.
Another example² is a loss of power in hover: the stabilising effect results in a pitch down moment generating forward descent, which is a better starting point for an autorotation than a backwards nose up descent.
So, the rotors in an intermeshing design rotate as they rotate because this increases the longitudinal stability of the helicopter.

¹ all pictures from Wikipedia, modified by me.
² thanks to @qqjkztd.

Probably, an important issue is the retreating blade stall.

Thanks for the excellent explanation! These are all points I had not considered!

@xxavier Can you elaborate how this is an issue here? I was under the impression that this was less of an issue for a helicopter with counterrotating rotors?

@flawr In an intermeshing-rotor helicopter, like the Flettner Kolibri or the Kamans, it makes a big difference if the 'outer blades' move forwards or backwards, because, if they move backwards, the lateral overturning moment in the case of retreating-blade stall could be severe...

The correct explanation is the incomplete torque compensation because of the tilted shafts. The torque vectors of each rotor have a large z-component and a small component in y-direction. The y-components are not compensated since they have the same sign for both rotors.
As a result a net pitch-up moment is generated which is increasing longitudinal stability. It would be the opposite if rotation direction are reversed.

I don't know exactly how that intermeshing rotors work, but I assume that the animation in this video is representing the actual situation which the engine turn the helical gear of the right rotor (left or right is determined by the pilot's arm when sitting the seat). The engine creates torque to the left side of the tail, but then it is cancelled by the interconnecting spur gear. By so, the net torque is zero. That's why there is no tail rotor as in normally helicopter. But however, there is gyroscopic precession created by each rotor. Both the rotors will push the nose down (pitched down). So, the helicopter must be already designed to slightly tend to the nose so the thrust they crated will cancel the gyroscopic precession. So to answer your question, will be any noticeable effect if one an identical intermeshing-helicopter but the rotors are rotated in the opposite direction, then my answer is: there is, as the helicopter will be pushed the tail down (pitch up), just the opposite of another one.

The two rotors rotate in opposite directions so the gyroscopic precession should be one the opposite of the other one and should cancel each other out.


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What is the real impact of biofuels on aviation?
I have seen tons of initiatives about using biofuels (like the ASTM D7566), but it is operative at large scale?, there is background info about demonstrative flights, but I don’t see a manufacturer or airline that is making use of the biofuel in regular basis.
It is a viable way of operate or it is a nonviable idea?

It is viable, but still much more expensive than traditional fuels, which is why nobody really uses it. Many of today's jets can run bio-fuel, but since it is in such short supply, it is much more expensive than regular fuel. With price competition, even a few cents per gallon can mean huge differences in fares.

The "real" (or at least ideal) impact of biofuels in aviation is a reduction in CO2 emissions. When they burn, they produce exactly the same amount of CO2 as fossil fuels, but, all this CO2 came from CO2 that was already in the atmosphere. So it's only putting back what was already there:

From the standpoint of human-released carbon dioxide, other greenhouse gas emissions, and contributions to climate change biofuels have one large advantage over gasoline, diesel and other fossil fuels: The feedstocks for biofuels are part of the above-ground carbon cycle. Unlike petroleum or coal, the soybeans, corn, switchgrass and other biological materials that are made into biofuels are not dug up from underground, nor do they release long-stored carbon as carbon dioxide into the atmosphere when burned. Instead, when biofuels are burned, carbon dioxide they recently captured is release back into the atmosphere.

This is sometimes claimed to mean biofuels are carbon neutral. For example, it's claimed here a 95% reduction occurs. But it's a bit more complex than that:

Producing biofuel with crops like corn often requires converting land from food to fuel production or destroying natural ecosystems that provide valuable services, including carbon sequestration. Crops also require fertilizers, pesticides and large amounts of water, as well as machinery for planting, growing, harvesting, transporting and processing. If forests are cleared for fuel crops and if the entire lifecycle of the fuels is taken into account, biofuels don't always reduce overall greenhouse gas emissions. Palm oil, used for biodiesel, is especially bad, because valuable carbon sinks like peat bogs and rain forests are often destroyed to grow palms.

As noted by Wikipedia, bio-fuel remains more expensive than traditional fuels.  A medium sized airline such as Jet Blue spends something like \$1 billion per year on fuel.  So if bio-fuel is a mere 1% more expensive (i.e. a few cents as mentioned by Ron), that costs them an extra \$10 million per year.

Yes it is viable, but like all new processes will need to go through the cycle of R&D, then scaling up production and distribution, then obtaining economy of scale. Cost is always a driving factor in the succes of a product, both for businesses and consumers.
The traditional oil refining industry has a lead and experience of over a century in tackling and solving the problems associated with large scale logistics: there is a lot of aviation fuel that needs to be shipped and trucked around the world. They could start this in a time when they could focus only on economical problems, not environmental ones. Shell sold its refinery in the Netherlands Antilles in the 1980s: it was set up in the 1910s, supplied the majority of aviation fuel to the allied air forces in WW2, and was very much up for a total rebuild to comply with present day duty of care. A sale of the refinery for one dollar to the Venezuelan state oil company PDVSA was deemed the best solution at the time.
So biofuel logistics needs to tackle the same logistical problems that conventional logistics has a century old headstart in, using technologies untried at this scale, and will have much higher production costs than traditional processes. In countries where a large part of fuel cost is made up by taxes, the government can play a beneficial role here.


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What type of batteries are used in airline planes?
In Embraer 145 and Boeing 777
I mean material, recharge cycle,  nominal current and voltages. From the comments I don't understand the difference if the plane is turboprop or turbofan.

What size plane? 747? Cessna? Somewhere in between?

Are you looking for battery capacities or discharge profiles for a start (assuming an S/G on smaller turbofans and turboprops). Your question just isn't very clear on what you are looking for.

Is your question about the batteries being Li-ion or Lead acid, etc, as explained here?

From this Concorde battery page, the Embraer E-145 can use a 44 Ah, 24 VDC Lead-Acid batter: Concorde RG-422
The Embraer E-145 can also use Ni-Cd batteries.
The Boeing 777 uses Ni-Cd batteries as well: Boeing 777 Saft Batteries


text:
"Get a box" article?
Been in "professional" aviation for 20Y. I recall an article where the author, an aviation manager, advocated for keeping a box in your office, for the purpose of packing all of your personal things the moment the job turned into something you didn't like / it wasn't supposed to be.
The overarching message was that your boss(es) needed to know that if your job became about something other than aviation safety, or whatever it's supposed to be, you're ready and willing to walk away at the drop of a hat.
Does anyone else remember this article and where it was published?

never heard of it, could apply to any business. But in reality it is more likely to give your boss the impression you're "not invested in the company" and "unreliable", excuses to fire you at the next performance review.

As a mind-set it might be beneficial, but I have a hard time seeing how keeping an actual physical box in your office would be valuable. Being willing to walk at any time is great but it's not like jobs don't know how to handle people resigning, and that includes how to get all their personal stuff out the door

This would appear to be just as applicable (or in applicable) to any job inside or outside aviation.

All good points. I think the article was from ~20Y ago when small to medium sized aviation operations were being told by customers and insurance companies that they had to have a director of safety, and DOs were hiring Safety mgrs to appease the requirements, but didn't want to hear a peep out of them. The collandar of my mind doesn't fully retain the article which is why I'd love to re-read it to see how accurately I recall it.


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Data protocol in helicopter's ARINC 717
I am presently doing a project where in I want to transfer certain aircraft parameters (helicopter) to a ground station where I would like to monitor them (establish a data link). I have thought of passively tapping them from the data bus between DIU unit and FDR which uses ARINC 717 protocol. Could I have some guidance on how to go about this?


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What is the overhaul interval for the spoiler mixer on the B737NG?
I've read that the overhaul interval is 12,000 FH, but then I heard the spoiler mixer is only removed from the aircraft if it's damaged. Which is correct?

Where did you read it?


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How can I calculate the fuel consumption of an Airbus 320-200 at various loads?
I want to know:

What is the fuel consumption of an Airbus A320-200 - 180 Seats, at 100% load factor for a distance of 2000 km?
What is the fuel consumption of an Airbus A320-200 - 180 Seats, at 80% load factor for a distance of 2000 km?

Welcome to Aviation:SE!

If you need precise values, you need to provide much more detail. Fuel consumption is affected by many parameters; see this answer for more detail.
For a precise estimate it will be best to employ a simulation software; see the answers to this question for more detail.
If you are just interested in a general estimate, the venerable Breguet equation will already give good results. First we need to know how much difference the 20% in load factor makes: The average mass of a passenger plus baggage for short-range trips is 100 kg, so the zero-fuel mass would be OEW + 18 t = 60.6 t in the 100% case and 3.6 tons less in the 80% case. Allow for 3 t of fuel reserves and plug that into the Breguet equation, using a fuel burn of $b_f$ = 0.000018 kg/Ns and a speed of Mach 0.78, which equates to $v$ = 262 m/s in 11.000 m altitude:
$$m_1 = m_2 \cdot e^{\frac{R\cdot g\cdot b_f}{v\cdot L/D}}$$
The L/D should be 18 and for the range we use R = 2000.000 m. $m_1$ is take-off mass and $m_2$ landing mass. This gives $m_1$ = 68.54 t for the 100% case and $m_1$ = 64.66 t for the 80% case. To be realistic, you would need to include different fuel flow during climb and descent, but the real value shouldn't be too far from the 5 rsp. 4.7 tons we get from the Breguet equation.
Note that when you repeat the calculation for 5,700 km range, the take-off mass comes out at 78.7 t for the 100% load factor, which is almost exactly the MTOW of the A-320. With 2.3 t of reserves, the Breguet equation gives you exactly the specified performance of the A-320-200. This should give you some confidence in those results.

how to understand, what is "e" in that equation?

@user54312, Euler's number e ≈ 2.71828.

There are a lot of factors that affect the fuel consumption. To answer your question, we have to make some assumptions.

Cruise altitude = 35000 ft.
Aircraft flown at LRC (Long range cruise speed).
Air conditioning normal flow.
Anti icing off.

In the A320 FCOM there are tables which shows fuel burn and distances covered from brake released to the landing. 2000 km is about 1080 nm and only the heaviest A320-200 can carry 180 passengers. This variant has a maximum take off weight of 78000 kgs.

As we do not have exactly 1080 nm in the table, we have to interpolate. So, at 35000 ft:
5961 kg + 6089 kg = 6025 kg
Now, we have to make adjustments to this figure to find the fuel burn at 78000 kg. Using the fuel correction column.
65 kg + 67 kg = 66 kg
The table is made for an aircraft with a weight of 55000 kg. If there is a fuel burn increment of 66 kg for every 1000 kg increase in weight, then for 78000 kg.
78000 kg - 55000 kg = 23000 kg So,
23 kg * 66 kg = 1518 kg.

The final fuel burn for an A320 weighing 78000 kgs over a 1080 nm flight is (6025 kg + 1518 kg), which is equal to: 7543 kg

If the aircraft weighs 80% of its maximum take off weight - 62400 kg
The calculation remains the same. We just need to correct it for the new weight. So,
62400 kg - 55000 kg = 7400 kg.
7.4 kg * 66 kg = 488.4 kg.

The final fuel burn for an A320 weighing 62400 kgs over a 1080 nm flight is (6025 kg + 488.4 kg), which is equal to: 6513.4 kg


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Why Cessna 152 has different airfoils at the root versus at the tip of the wing?
I recently read that C152 have two different airfoils on its wing. NACA 2412 at the wing root and NACA 0012 the wingtip. Why? And why are those particular airfoils (with their inherent aerodynamic properties) installed at the root and the other at the tip?

At the end you'll find the answer to the question plus a short question to verify if I've made myself clear ;-)

An airfoil can be basically described by 3 parameters:

the shape/curvature of its camber line;
the radius of its leading edge (the trailing edge is almost always pointy);
the distribution of the thickness upon the camber line.

Those 3 parameters are enough to define any airfoil of practical use (source Wikipedia):

Without any claim to thoroughness (that would cover an entire book) the following can be said:

A rounder leading edge and higher thickness (>10% of the chord) give a smooth stall with a progressive loss of lift; pitching moment also changes smoothly approaching the stall region; thick airfoils have also a big volume that can be used for fuel and structure $\rightarrow$ good for the root of the wing or of a propeller.
A thinner leading edge/thickness gives a more nervous stall with a higher pitching moment variation; anyway at high subsonic speeds a thinner airfoil possesses a lower drag than a thick one since it retards the formation of shock waves (which give rise to the boundary layer's detachment and stall); being thinner, it also weight less $\rightarrow$ good for the tip.
At low subsonic speeds, a thickness of 12% is the sweet spot to have the highest L/D ratio.
A pointy leading edge is necessary at supersonic speeds in order to avoid the formation of a detached (aka bow) shock which increases drag and temperature $\rightarrow$ virtually all the wings of supersonic fighters are built around a very thin, pointy airfoil; the loss in internal volume for fuel and structure is compensated for by the use of delta planform for the wing.
Camber is mainly used to control/delay stall and limit pitching moment; a very pronounced camber (one that makes the airfoil look like an arc) is used when lift needs to be generated at very high AoA i.e. low speeds; this is typically the shape that a bird's wing possesses or that a wing assumes when its high-lift devices are deployed; in those cases a round, thick leading edge helps too, as already said; anyway a lot of camber doesn't work at high speeds since the boundary layer tends to detach and make the airfoil stall (the only exception being turbine/compressor blades); as a side effect, an airfoil with high camber generates also a high pitching moment which needs a lot of structure to be carried (to partially offset this, the camber can be built in such a way to go upward toward the trailing edge in a sort of "S" shaped pattern; in this way the good aerodynamic characteristics at high AoA are retained but without the increased torsional moment).
In order to aerodynamically and structurally optimise the wing, the spanwise lift distribution should become lower and lower toward the wing tips.

All that being said, we can now better understand the airfoils choice on many airplanes. In particular for the C152 we have that:

Both the root and the tip have the same thickness of 12% $\rightarrow$ see point 1 and 3. Plus, having the same thickness, manufacturing might be simplified.
Being cambered, the airfoil at the root (NACA 2412) generates more lift and that, combined with the flaps, gives good stall and low speed characteristics; the higher pitching moment due to the camber is structurally not a problem being the airfoil thick (more space for the structure) and close to the fuselage (it doesn't have to travel along the whole wing) $\rightarrow$ see point 5.
At the same AoA, the uncambered airfoil at the tip (NACA 0012) delivers less lift than the cambered airfoil (NACA 2412) at the root $\rightarrow$ see point 6.

Let's see if I've made myself clear and why, for example, the B-52 used a NACA 63A219 for the root and a                  NACA 65A209 for the tip; or why the F-18 uses a NACA 65A005 for the root and a NACA 65A003 for the tip?

Thnk you for explanation, one more question: shouldn't a cambered airfoil be placed at the wing tip so that the wing root stalls first and ailerons remain functional as long as possible?

Yes right. I'm not sure but the C152 should have a couple of degrees twist so that the tip stalls after the root.

It was silly of me to think I could answer this question with such a limited knowledge. Great answer. I'll stick to what I actually know in future :D

@Jamiec: we are all here to learn from each other


text:
Why does using carburetor heat increase fuel consumption?
As written above, why does using carburetor heat increase fuel consumption? Because I found such information in a few SOPs for piston airplanes and I do not understand why does it happen

Why not include one of the SOPs in your question?

Those are in polish so hardly anybody will understand. There are just tables with fuel consumption with and without carb heat and those with carb heat have higher values. Maybe those tables are wrong, I don't know, I hope somebody here knows ;)

Using carb heat means hotter, less dense air is sent to the carburetor (to clear ice).  This would change the fuel/air mixture.  It would depend where you were on the "lean to rich curve".  There is a possibility, if the engine ran too hot, the fuel mixture might have to be made more rich, affecting miles per gallon efficiency.  What type of engine are we talking about here?

It is a Rotax 912

It's worth remarking that in practical terms carb heat can actually reduce fuel consumption, if it results in the fuel/air mixture being better distributed across the engine cylinders. This is something which Mike Busch has demonstrated when finding techniques to run engines lean-of-peak. The heat helps vaporize the fuel, ensuring that the liquid fuel doesn't favor one intake pipe over another.

I found an english version of this SOP , screenshot added

I can think of two reasons:

The efficiency of heat machines depends on the difference between lowest and highest temperature in the cycle, relative to the highest temperature, as formulated first by Sadi Carnot. Simply put, the efficiency cannot be larger than $$\eta_{max}≤\frac{T_{max}-T_{min}}{T_{max}}$$
where all temperatures are expressed relative to absolute zero. If the entry temperature $T_{min}$ is raised by carburetor heat, the value of $\eta$ will drop. For the nitpickers: Piston engines are best described by the Otto cycle which uses an isochoric addition of heat and is a bit more messy to describe than the ideal Carnot cycle. If you want to include Diesel engines, use the Trinkler or Seiliger cycle.
With the higher entry temperature, all temperatures in the cycle are higher and you need to lean less in order not to exceed the desired cylinder head and exhaust gas temperatures. More fuel is needed for cooling, so the richer mixture will drive up fuel consumption.

I have a funny thought concerning the cycle: why can't we include the carburetor heat as part of the cycle, and keep T_amb = T_min? Ultimately, part of the heat  that we put into the carburetor will be even extracted during the expansion (at engine efficiency), wouldn't it? And if we used exhaust heat for the carburetor (which would just be wasted otherwise), wouldn't we even increase the efficiency?

@CarlBerger A funny thought indeed. But you want to first compress, then add heat. If you look at the T-s-diagram of the Otto cycle, you want to maximize the enclosed area relative to the area between x-Axis and the diagram plus the enclosed area. Initial heat will only shift the enclosed area up and increase exhaust heat, which is wasted. Or take the the p-v-diagram: Initial heating will shift it right (lower density) while pressures stay the same. Shifting the process right reduces the enclosed area and, therefore, the work that can be extracted. Better to add this heat after compression …

yes obviously.. I guess i shouldn't write comments that late at night.

Heating the air causes the air to be less dense.
We all know that as you climb, the air becomes less dense and you have to lean the mixture for better performance and fuel economy. This also applies to Carb Heat. If you don't lean the mixture after applying Carb heat, the mixture will be richer and fuel economy will be reduced.

That’s the point that I do not understand. Ofc hotter air is less dense, so with the same amount of fuel the mixture will be overally richer. But on Rotax 912 there isn’t any manual mixture adjustment lever/knob, so why does the fuel consumption increase since we are not able to do any mixture adjustments

@Konrad If you do nothing but heat the intake air, the fuel consumption does not change, but the engine power drops.  If you were flying trimmed and level, then turned on carb heat but did nothing else, you would start to lose altitude because the engine would no longer be producing as much power as it was before (the now rich mixture being unable to burn all the fuel it could just moments ago).  If you don't want to fall out of the sky, you will increase the throttle - burning more fuel than before now to hold altitude.

If there’s no manual mixture adjustment then the reduction in fuel viscosity may increase the flow rate, this may be more significant than the reduction in fuel density

@J... - That, in itself, is an answer. You should make it one instead of just a comment.

I don't know the detail of the Rotax, but if the pilot doesn't have an adjustment knob in the cockpit, it doesn't necessarily mean that the value isn't adjusted.
For unchanged mixture though, the reduced air mass flow means less power- and if you have to drive the engine to a higher powered operating point, that might be less economic.
I guess we have too many technical possibilities for different engines that make a single general answer quite difficult..